Lisp 函数错误地返回Nil

Lisp 函数错误地返回Nil,lisp,common-lisp,read-eval-print-loop,sbcl,Lisp,Common Lisp,Read Eval Print Loop,Sbcl,我现在正试图学习Lisp,作为CS1课程的补充,因为课程对我来说太慢了。我学习了《实用通用Lisp》,到目前为止,这本书是一本很棒的书,但我在获得一些示例时遇到了一些困难。例如,如果我将以下文件加载到REPL中: ;;;; Created on 2010-09-01 19:44:03 (defun makeCD (title artist rating ripped) (list :title title :artist artist :rating rating :ripped ripp

我现在正试图学习Lisp,作为CS1课程的补充,因为课程对我来说太慢了。我学习了《实用通用Lisp》,到目前为止,这本书是一本很棒的书,但我在获得一些示例时遇到了一些困难。例如,如果我将以下文件加载到REPL中:

;;;; Created on 2010-09-01 19:44:03

(defun makeCD (title artist rating ripped)
  (list :title title :artist artist :rating rating :ripped ripped))

(defvar *db* nil)

(defun addRecord (cd) 
  (push cd *db*))

(defun dumpDB ()
  (dolist (cd *db*)
    (format t "~{~a:~10t~a~%~}~%" cd)))

(defun promptRead (prompt)
    (format *query-io* "~a: " prompt)
    (force-output *query-io*)
    (read-line *query-io*))

(defun promptForCD ()
    (makeCD
        (promptRead "Title")
        (promptRead "Artist")
        (or (parse-integer (promptRead "Rating") :junk-allowed t) 0)
        (y-or-n-p "Ripped [y/n]: ")))

(defun addCDs ()
    (loop (addRecord (promptForCD))
        (if (not (y-or-n-p "Another? [y/n]: ")) (return))))

(defun saveDB (fileName)
    (with-open-file (out fileName
            :direction :output
            :if-exists :supersede)
        (with-standard-io-syntax 
            (print *db* out))))

(defun loadDB (fileName)
    (with-open-file (in fileName)
        (with-standard-io-syntax
            (setf *db* (read in)))))

(defun select (selectorFn)
    (remove-if-not selectorFn *db*))

(defun artistSelector (artist)
    #'(lambda (cd) (equal (getf cd :artist) artist)))
并使用
(选择(artistSelector“the Beatles”)
查询“数据库”),即使我在数据库中确实有一个条目,其中
:artist
等于
“the Beatles”
,函数返回
NIL

我在这里做错了什么?

没什么,AFAICT:

$ sbcl This is SBCL 1.0.34.0... [[pasted in code above verbatim, then:]] * (addRecord (makeCD "White Album" "The Beatles" 5 t)) ((:TITLE "White Album" :ARTIST "The Beatles" :RATING 5 :RIPPED T)) * (select (artistSelector "The Beatles")) ((:TITLE "White Album" :ARTIST "The Beatles" :RATING 5 :RIPPED T)) $sbcl 这是SBCL 1.0.34.0。。。 [[逐字粘贴在上面的代码中,然后:] *(addRecord(制作CD“白色专辑”“披头士”5T)) (:标题“白色专辑”:艺术家“披头士”:评级5:T)) *(选择(艺人选择“披头士”)) (:标题“白色专辑”:艺术家“披头士”:评级5:T))
请注意,EQUAL是区分大小写的,当然,如果您从未调用addRecord,那么select将返回NIL。好的,当我通过
addCDs
函数添加记录时,问题似乎会出现,但当我直接调用
addRecord
时,问题就不会出现了。我已经解决了。使用
addCDs
函数时,您不会在引号中输入字符串。Heh。我完全错过了
(addcd)
。我查找
选择
,如问题中所示,然后回过头来看看我需要如何称呼它。哎呀!
CL-USER 18 > (addcds)
Title: Black Album
Artist: Prince
Rating: 10
Title: White Album
Artist: The Beatles
Rating: 10
NIL

CL-USER 19 > (select (artistSelector "The Beatles"))
((:TITLE "White Album" :ARTIST "The Beatles" :RATING 10 :RIPPED T))